1. Field of the Invention
The invention relates to a cable duct made up of plastic troughs, which can be lined up in a row next to one another, and to an elevated cable duct, and to covers therefor.
2. Discussion of the Prior Art
Plastic cable ducts with approximately U-shaped troughs which are provided with a cover are known from WO 94/21018. These troughs, which can be endlessly lined up in a row next to one another and are provided with connectors, are injection molded, predominantly from recycled plastic, such as polyester, polyurethane or polyethylene, in lengths measuring approximately 1 m. These troughs are equipped with special ribs and protrusions which allow such ducts to be buried in the ground, in particular along railroad routes. It is possible to walk on the cover.
A brochure published by Krupp, DE, and entitled "Der Kunststoffkabelkanal DRAE-KA" discloses the practice of elevating such cable ducts in marshland. The brochure sets forth a wood pile with boards which extend thereon from pile to pile and serve as a supporting structure for the cable duct. Of course, exposure to weathering means that such a supporting structure has only a very short service life.
German references DE 39 36 003 C2 and DE 34 47 836 A1 disclose elevated cable ducts in the case of which trough-like sheet-metal cable-duct elements are screwed to metal supports and transverse securing means provided thereon. Both the supports and the transverse load-bearing members as well as the troughs, which are all screwed to one another, are connected at short spacings to the parallel rail track by corresponding grounding cables. This measure is necessary both because it is possible for the cables in the trough to become defective, and thus for the entire cable duct to become conductive, and because, in the case of a contact wire of an electric railroad rupturing, the formation of parasitic voltages is possible, and this has to be prevented. Nevertheless, in the meantime, the railroad companies no longer allow such sheet-metal ducts on electrified stretches of track. Operators who happen to be present could be put in danger by current surges and corresponding conduction of the ducts; moreover, problems may arise as far as signalling is concerned, in particular for the presence-of-trains indicating system.
Although cable ducts which are known from WO 94/21018 have been used successfully when buried in the ground, their application area is limited, e.g. in tunnels or where water build-up is to be expected and in cases of flush out and stretches where embankment slippage is to be expected.